Diameter Credit Control Application (DCCA) is a control protocol for online charging, which was designed by the Internet Engineering Task Force (IETF) and expanded by the 3rd Generation Partnership Project (3GPP). DCCA is based on a client terminal (prepayment client terminal or PPC)/server (prepayment server or PPS) mode. Within DCCA, a PPC is designed as in the same network unit as an anchor point. When a user moves within a 3G network, since the anchor point of a GPRS gateway-supported node does not change, the PPC does not change. Therefore, it is not necessary to consider the issue of mobility while using such network architecture for charging, as shown in FIG. 1.
However, as the network becomes flatter and flatter, some online charging functions have been transferred to, for example, access points of an Access Service Network Gateway of a WiMAX network (ASN GW) instead of focusing only on anchor points, as shown in FIG. 2 which illustrates a Diameter online charging architecture in a WiMAX network. When a user is moving, the mobile station may move from one ASN GW/PPC to another ASN GW/PPC. In this case, the prepayment client terminal shall be relocated, and also the charging continuity shall be maintained to support the continuity of a user session. Current DCCA is obviously not capable of solving this problem.